使用flex和bison创建过滤器
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假设我们有一个类具有一些属性。这个类有很多实例。给定一个过滤的规则，挑选符合规则的实例。
假设规则使用类似C语言的语句进行描述。
例子：
属性列表
width int
height int
fps float
os string
一种可能的过滤器：
width > 640 || height < 450
1. 构造词法器
filter.l
%{#include <stdio.h>#include <stdlib.h>// override inputextern int readInputForLexer(char* buffer, size_t *numBytesRead, int maxBytesToRead);#undef YY_INPUT#define YY_INPUT(b,r,s) readInputForLexer(b, &r, s)#include "filter.tab.h"void yyerror(char *); // need declare this func// yytext: current match, string// modify yylval (of type YYSTYPE; optional) and return component type%}%%[\t\n ] ;[0-9]+ { yylval.iVal = atoi(yytext); return INTEGER; }[0-9]*\.[0-9]+ { yylval.fVal = atof(yytext); return FLOAT; }[a-zA-Z/][a-zA-Z/0-9]* { yylval.sVal = strdup(yytext); return ID; }[\+\-\*\/\%] { return *yytext; }== { return EQ; }\> { return GT; }\< { return LT; }\>= { return GE; }\<= { return LE; }!= { return NEQ; }\|\| { return OR; }\&\& { return AND; }\( { return '('; }\) { return ')'; }\"(\\.|[^\\"])*\" { yylval.sVal = strdup(yytext); return STRING; }. { yyerror("Bad character"); }%%// https://www.ibm.com/developerworks/cn/linux/sdk/lex/// used for multiple source files. here simply return 1 to// stop parse at EOFint yywrap(void){ return 1;}2. 创建yacc文件
%{/* Created by Zhenyong Chen, 2017/07/30 * * This demo is going to create a tree structured filter. * A has a list of properties * There's a set of rules * The filter will check whether A is qualified * */#include <stdlib.h>#include <stdio.h>#include <string.h>#include <memory.h>#include "syntax.h"#undef YYLEX_PARAMextern int yylex();void yyerror(char *);static Operand *_outputTree = NULL;%}// http://www.gnu.org/software/bison/manual/html_node/Token-Decl.html// override default YYSTYPE (YYSTYPE yylval in lex file)%union { float fVal; int iVal; char *sVal; struct Operand *synNode;}%token <iVal> INTEGER "int"%token <fVal> FLOAT "float"%token <sVal> ID%token EQ "=="%token NEQ "!="%token GT ">"%token LT "<"%token GE ">="%token LE "<="%token OR "||"%token AND "&&"%token <sVal> STRING%left '+' '-'%left '*' '/' '%'// tell parser the nonterminal node type%type<synNode> program%type<synNode> expr%type<synNode> AndExpr%type<synNode> OrExpr%%// $$, $1, ... are of type YYSTYPE (http://pubs.opengroup.org/onlinepubs/7908799/xcu/yacc.html)program: OrExpr { $$ = $1; _outputTree = $$;} | { $$ = NULL; _outputTree = $$; } // could be empty program ;expr: ID "==" STRING { $$ = Operand::CreateNonTermNode(Operand::OP_EQ, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); free($3); } | ID "!=" STRING { $$ = Operand::CreateNonTermNode(Operand::OP_NE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); free($3); } | ID "==" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_EQ, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "!=" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_NE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "==" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_EQ, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "!=" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_NE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID ">" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_GT, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID ">" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_GT, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "<" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_LT, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "<" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_LT, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID ">=" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_GE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID ">=" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_GE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "<=" INTEGER { $$ = Operand::CreateNonTermNode(Operand::OP_LE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | ID "<=" FLOAT { $$ = Operand::CreateNonTermNode(Operand::OP_LE, Operand::CreateVarNode($1), Operand::CreateValueNode($3)); free($1); } | '(' OrExpr ')' { $$ = $2; } ;AndExpr: expr { $$ = $1; } | AndExpr AND expr { $$ = Operand::CreateNonTermNode(Operand::OP_AND, $1, $3); } ;OrExpr: AndExpr { $$ = $1; } | OrExpr "||" AndExpr { $$ = Operand::CreateNonTermNode(Operand::OP_OR, $1, $3); } ;%%void yyerror(char *s){ printf("Compile error: %s\n", s);}static char *_buf = NULL;static int _readOffset = 0;int readInputForLexer(char* buffer, size_t *numBytesRead, int maxBytesToRead){ int numBytesToRead = maxBytesToRead; int bytesRemaining = (int)strlen(_buf) - _readOffset; if(bytesRemaining == 0) { *numBytesRead = 0; return -1; } if (numBytesToRead > bytesRemaining) { numBytesToRead = bytesRemaining; } memcpy(buffer, _buf+_readOffset, numBytesToRead); *numBytesRead = numBytesToRead; _readOffset += numBytesToRead; return 0;}Operand *parseProgram(const char *text){ if(text == NULL) return NULL; _buf = (char *)malloc(strlen(text) + 64); strcpy(_buf, text); _readOffset = 0; _outputTree = NULL; yyparse(); free(_buf); _buf = NULL; Operand *ret = _outputTree; _outputTree = NULL; return ret;}3. 语法树
syntax.h
#if !defined(__SYNTAX_H__)#define __SYNTAX_H__#include <string>class Operand {public: enum OperatorType { OP_AND = 1, OP_OR, OP_EQ, OP_NE, OP_GT, OP_LT, OP_GE, OP_LE, }; enum OperandType { OP_NONTERM = 0, OP_INT, OP_FLOAT, OP_STRING, OP_VAR, }; enum OperandType eType; // if OP_NONTERM enum OperatorType eOperator; Operand *aOperands[2]; // if OP_VAR std::string varName; // otherwise, values int iVal; float fVal; std::string sVal; // create a leaf node: int/float/string static Operand *CreateValueNode(int ival); static Operand *CreateValueNode(float fval); static Operand *CreateValueNode(const char *sval); static Operand *CreateVarNode(const char *name); // create a non-terminal node static Operand *CreateNonTermNode(enum OperatorType opType, Operand *operand1 = NULL, Operand *operand2 = NULL); virtual ~Operand(); void Dump(int margin);private: Operand();};#endif /* __SYNTAX_H__ */syntax.cpp
#include "syntax.h"Operand::Operand(){ eType = OP_INT; iVal = 0;}Operand::~Operand(){ if(eType == OP_NONTERM) { for(int i=0; i<sizeof(aOperands)/sizeof(aOperands[0]); i++) { if(aOperands[i] != NULL) { delete aOperands[i]; aOperands[i] = NULL; } } }}Operand *Operand::CreateValueNode(int ival){ Operand *op = new Operand(); op->eType = OP_INT; op->iVal = ival; return op;}Operand *Operand::CreateValueNode(float fval){ Operand *op = new Operand(); op->eType = OP_FLOAT; op->fVal = fval; return op;}Operand *Operand::CreateValueNode(const char *sval){ Operand *op = new Operand(); op->eType = OP_STRING; op->sVal = sval; return op;}Operand *Operand::CreateVarNode(const char *name){ Operand *op = new Operand(); op->eType = OP_VAR; op->varName = name; return op;}Operand *Operand::CreateNonTermNode(enum OperatorType opType, Operand *operand1/* = NULL*/, Operand *operand2/* = NULL*/){ Operand *op = new Operand(); op->eType = OP_NONTERM; op->eOperator = opType; op->aOperands[0] = operand1; op->aOperands[1] = operand2; return op;}static void print_margin(int margin){ while(margin > 0) { printf(" "); margin--; }}const char *operatorTypeToString(enum Operand::OperatorType t){ switch(t) { case Operand::OP_AND: return "&&"; case Operand::OP_OR: return "||"; case Operand::OP_EQ: return "=="; case Operand::OP_NE: return "!="; case Operand::OP_GT: return ">"; case Operand::OP_LT: return "<"; case Operand::OP_GE: return ">="; case Operand::OP_LE: return "<="; default: return "ERROR"; }}void Operand::Dump(int margin){ if(eType == OP_NONTERM) { print_margin(margin); // print operator printf("%s {\n", operatorTypeToString(eOperator)); for(int i=0; i<sizeof(aOperands)/sizeof(aOperands[0]); i++) { if(aOperands[i] != NULL) { aOperands[i]->Dump(margin + 4); } } print_margin(margin); printf("}\n"); } else { print_margin(margin); switch(eType) { case OP_INT: printf("%d\n", iVal); break; case OP_FLOAT: printf("%f\n", fVal); break; case OP_STRING: printf("%s\n", sVal.c_str()); break; case OP_VAR: printf("%s\n", varName.c_str()); break; default: break; } }}4. 使用方法
main.cpp
#include <stdio.h>#include "syntax.h"#include <string>#include <list>extern Operand *parseProgram(const char *text);// evaluate synstax treestruct compoundValue { int type; // 0: void; 1: int; 2: float; 3: std::string; 4: bool int iVal; float fVal; std::string sVal; bool bVal;};void printValue(struct compoundValue &v){ if(v.type == 1) { printf("(int)%d\n", v.iVal); } else if(v.type == 2) { printf("(float)%f\n", v.fVal); } else if(v.type == 3) { printf("(string)%s\n", v.sVal.c_str()); } else if(v.type == 4) { printf("(bool)%s\n", v.bVal ? "true" : "false"); } else { // should not reach here }}// define several variablesstruct variable { std::string name; struct compoundValue value;};std::list<struct variable> gVariableList;void initVarList(){ struct variable v; v.name = "width"; v.value.type = 1; // int v.value.iVal = 640; gVariableList.push_back(v); v.name = "height"; v.value.type = 1; // int v.value.iVal = 360; gVariableList.push_back(v); v.name = "fps"; v.value.type = 2; // float v.value.fVal = 25.0; gVariableList.push_back(v); v.name = "os"; v.value.type = 3; // std::string v.value.sVal = "Android"; gVariableList.push_back(v); v.name = "enabled"; v.value.type = 4; // bool v.value.bVal = true; gVariableList.push_back(v);}int get_variable_type(std::string varName){ std::list<struct variable>::iterator it; for(it=gVariableList.begin(); it!=gVariableList.end(); it++) { struct variable &v = *it; if(v.name.compare(varName) == 0) { return v.value.type; } } return -1; // should not reach here}int get_variable_value_i(std::string varName){ std::list<struct variable>::iterator it; for(it=gVariableList.begin(); it!=gVariableList.end(); it++) { struct variable &v = *it; if(v.name.compare(varName) == 0) { return v.value.iVal; } } return 0; // should not reach here}float get_variable_value_f(std::string varName){ std::list<struct variable>::iterator it; for(it=gVariableList.begin(); it!=gVariableList.end(); it++) { struct variable &v = *it; if(v.name.compare(varName) == 0) { return v.value.fVal; } } return 0.0f; // should not reach here}std::string get_variable_value_s(std::string varName){ std::list<struct variable>::iterator it; for(it=gVariableList.begin(); it!=gVariableList.end(); it++) { struct variable &v = *it; if(v.name.compare(varName) == 0) { return v.value.sVal; } } return ""; // should not reach here}bool get_variable_value_b(std::string varName){ std::list<struct variable>::iterator it; for(it=gVariableList.begin(); it!=gVariableList.end(); it++) { struct variable &v = *it; if(v.name.compare(varName) == 0) { return v.value.bVal; } } return false; // should not reach here}struct compoundValue eval_syntax(Operand &op){ struct compoundValue v; // traverse the tree if(op.eType == Operand::OP_INT) { v.type = 1; v.iVal = op.iVal; } else if(op.eType == Operand::OP_FLOAT) { v.type = 2; v.fVal = op.fVal; } else if(op.eType == Operand::OP_STRING) { v.type = 3; v.sVal = op.sVal; } else if(op.eType == Operand::OP_VAR) { v.type = get_variable_type(op.varName); if(v.type == 1) { v.iVal = get_variable_value_i(op.varName); } else if(v.type == 2) { v.fVal = get_variable_value_f(op.varName); } else if(v.type == 3) { v.sVal = get_variable_value_s(op.varName); } else if(v.type == 4) { v.bVal = get_variable_value_b(op.varName); } } else if(op.eType == Operand::OP_NONTERM) { if(op.eOperator == Operand::OP_AND) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; v.bVal = left.bVal && right.bVal; } else if(op.eOperator == Operand::OP_OR) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); v.type = 4; if(left.bVal) { v.bVal = true; } else { right = eval_syntax(*op.aOperands[1]); v.bVal = right.bVal; } } else if(op.eOperator == Operand::OP_EQ) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal == right.iVal); else if(left.type == 2) v.bVal = (left.fVal == right.fVal); else if(left.type == 3) v.bVal = left.sVal.compare(right.sVal) == 0; else if(left.type == 4) v.bVal = (left.bVal == right.bVal); } else if(op.eOperator == Operand::OP_NE) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal != right.iVal); else if(left.type == 2) v.bVal = (left.fVal != right.fVal); else if(left.type == 3) v.bVal = left.sVal.compare(right.sVal) != 0; else if(left.type == 4) v.bVal = (left.bVal != right.bVal); } else if(op.eOperator == Operand::OP_GT) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal > right.iVal); else if(left.type == 2) v.bVal = (left.fVal > right.fVal); } else if(op.eOperator == Operand::OP_LT) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal < right.iVal); else if(left.type == 2) v.bVal = (left.fVal < right.fVal); } else if(op.eOperator == Operand::OP_GE) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal >= right.iVal); else if(left.type == 2) v.bVal = (left.fVal >= right.fVal); } else if(op.eOperator == Operand::OP_LE) { struct compoundValue left, right; left = eval_syntax(*op.aOperands[0]); right = eval_syntax(*op.aOperands[1]); v.type = 4; if(left.type == 1) v.bVal = (left.iVal <= right.iVal); else if(left.type == 2) v.bVal = (left.fVal <= right.fVal); } } return v;}int main(int argc, const char **agrv){ initVarList(); const char *s = "width > 640 || height < 450"; printf("Input: \n%s\n", s); Operand *p = parseProgram(s); if(p != NULL) { p->Dump(0); struct compoundValue v = eval_syntax(*p); delete p; printf("Evaluated:\n"); printValue(v); } return 0;}6. 编译
#!/bin/bashbison -d filter.y && flex filter.l || exit 1g++ -o filter *.c *.cppexit 0
输出结果:
Input:
width > 640 || height < 450
|| {
> {
width
640
}
< {
height
450
}
}
Evaluated:
(bool)true
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